We show that the effective interaction potential between microwave-shielded polar molecules consists of an anisotropic van der Waals-like shielding core and a modified dipolar inter-action. This effective potential is validated by comparing its scattering cross-sections with those calculated using intermolecular potential involving all interaction channels. It is shown that a scattering resonance can be induced under microwave fields and a field-link tetramer bound state emerges. With the effective potential, we further study the Bardeen-Cooper-Schrieffer pairing in microwave-shielded molecular gas. We show that the superfluid critical temperature is drastically enhanced near the resonance.